Locomotor System: Muscles

Muscular System

Muscles in the head

• Frontal: it moves the scalp forwards. It raises eyebrows.  It wrinkles the forehead skin.
• Occipital: it moves the scalp backwards. It is joined to the frontal muscle by the aponeurosis that covers the upper part of the cranium. 
• Nasal: there are two nasal bones. They wrinkles the nose.
• Buccinator: it inflates the cheeks.
• Orbicularis oculis: it closes the eyes.
• Orbicularis oris: it closes and presses the lips together. It can also push them forwards.
• Risorius: it pulls the lip commissure sideways. Like smiling
• Supercilii: it pulls the internal part of the eyebrows down. Like frowning.
• Zygomatic major: it moves the extremes of the lips upwards. Like laughing.
• Masseter: it closes the mouth raising the mandible.
• Temporal: it raises and retracts the mandible. If one of them relaxes and the other contracts, the mandible moves laterally.
• Levator palpebrae superioris: it raises the upper eyelid.
• Levator lavi superioris: it raises the upper lip.
• Digastric: it raises the hyoid bone and descends the mandible to open the mouth.
• Mentalis: it raises the central part of the lower lip. 

Locomotor System: Muscular Function

Introduction

Muscles are responsible for providing the bodily movements. There are also muscles that do not move bones, but provide involuntary movements of internal organs, such as the peristaltic movements of the intestine and the contraction of blood vessels. Finally, when the muscles contract they produce heat (consuming energy).

There are three different types of muscle: smooth, cardiac and skeletal. When we are talking about the locomotor system, however, we are only referring to skeletal muscles, that provide general movements of the skeleton.

The muscular system is an important part of our body. It is 40 % of our total weight.

Structure of muscular fibres

All the skeletal muscles are surrounded by a layer made up of connective tissue called epimysium. The muscle is divided into fascicles by a connective membrane called perimysium. The fascicles are made up of several cells called muscular fibre. Each muscular fibre is surrounded by a thin connective membrane called endomysium. These three membranes join at the edge of the muscle. After the fusion of these membranes, the connective tissue becomes richer in elastic and cartilaginous fibres, forming the tendon. The tendon firmly connects the muscle to the bone.

Skeletal muscle.

The muscle cells that make up the skeletal muscles, called myocytes, are cylindrical and extremely long. Indeed, they can be more than five centimetres long. They have many nuclei, even more than one hundred nuclei per cell.